Finished flame-resistant textile materials



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US. Cl. 117-136 14 Claims ABSTRACT OF THE DISCLOSURE 15 An improvement is provided in the process for the finishing of filaments, fibres, yarns, threads and fabrics of flame-resistance cellulose acetate which has been produced by spinning from a solution containing cellulose acetate and a flame-proofing agent dispersed therein. The improvement comprises applying to the filaments, fibres, yarns, threads and fabrics a coating of an organic polymer composition which composition has a temperature of thermal decomposition not substantially greater than that of the flame-resistant cellulose acetate and which decomposes at its decomposition temperature to form soft and fusible products. The flame-proofing agent is I preferably a tris(polybro moaliphatic)phosphate and mostl preferably a tris(dibromopropyl)phosphate. The finish-{.30 ing composition may also contain a flame-proofing agent.

This invention relates to the production of finished flame-resistant textile filaments, fibers, yarns, threads and fabrics.

This application is a continuation of application Ser. No. 454,216, filed May 7, 1965 and abandoned since the filing of the present application, which application is in turn a continuation-in-part of application Ser. No. 155,161, filed Nov. 27, 1961, now abandoned.

It is known to incorporate certain flame-proofing agents into cellulose acetate in order to render fibres, yarns and filaments, and fabrics made therefrom, both flame-resistant and resistant to afterglow. Various halogenated compounds have been proposed for incorporation into the spinning dope from which the yarns, filaments or fibres are produced and it has also been proposed, for example in U .S. patent specification No. 2,660,543 to make flameresistant textile filaments, fibres, yarns and fabrics having a basis of cellulose acetate, the cellulose acetate spin ning solution from which the materials have been prepared containing a tris(polybromoaliphatic)phosphate having a bromine content of at least 50 percent by weight, in an amount from about 2.5 to 10 percent by weight of the cellulose acetate contained in the spinning solution. Such materials have effective flame-resistance and do not ex= hibit a substantial afterglow.

It is also known to prepare a flame-resistant cellulose acetate by coating an ordinary cellulose acetate material with a flame-resistant finish, for example as described in U.S. patent specification No. 2,779,691. Such a finish may readily be removed by laundering and the same patent provides for the coating of the flame-resistant material with a resin which may resist removal under laundering conditions.

Such resin coatings and dressing compositions for cel-: lulose acetate materials which are employed to impart, for example specific properties of handle and drape may require to be used on flame-resistant material for either of the purposes described, but in either case it is necessary to ensure that the dressing coin osition applied to a flamc= 3,471,318 Patented Oct. 7, 1969 resistant fabric shall not impair or destroy the flame resistance of the finished material.

It has, however, been found in practice that when flameresistant cellulose acetate materials are produced with a finish of either of these kinds, even if the finishing com position is present in a very small amount and indeed even if the finishing composition is itself flame-resistant or hea tgesistant, the finished flame-resistant material may burn freely when a flame is applied thereto.

It is necessary to distinguish between flame-resistant and heat-resistant materials. Fabrics such as those made from polyvinylidene chloride compositions, for example those sold under the tradename Saran are flame-resist ant since they will not take fire nor support combustion when held in the flame, but they are not heat-resistant in that they decompose readily when heated at about 180 C. Silicone polymers such as silicone rubber and silicone resin are heat-resistant in so far as they will withstand temperatures up to about 300 C. Such silicone polyers, however, may be flammable at their decomposition temperatures and are not therefore flame-resistant.

Fabrics made from cellulose acetate fibres which have been produced from filaments, fibers or yarns made by spinning from a solution containing such a flame-resistant additive as tris(dibromopropyl) phosphate are flameresistant but they are not heat-resistant, and indeed thedecomposition temperature of such fabrics is lower than that of those prepared from ordinary cellulose acetate.

When a fabric which is composed of cellulose acetate is held in a flame the fabric takes fire. Decomposition takes place at a temperature of about 200 C. giving about percent of volatile tarry matter, about 5 percent carbonaceous residue and about 15 percent of gases. The volatile tarry matter is readily combustible and the fabric takes fire and will continue to burn when removed from the source of flame. This could be described as the normal decomposition of cellulose acetate materials on heating. When, however, a flame-resistant cellulose acetate fabric, which may incorporate or be coated with any of the known phosphate flame-resistant additives, is held in a flame it will decompose and whilst it is in the flame the temperature willjbe above 200 C. so that normal decomposition may take place giving volatile tars which burn. When the burning fabric is removed from the flame its temperature falls and when it has dropped to about C., which usually occurs very rapidly, the flame goes out because at this temperature the decomposition prodnets are about 4 percent of volatile tarry matter, about 50 percent of carbonaceous residue and about 45 percent of gases, chiefly water vapour. During the cooling, propagation of the flame is resisted by the atmosphere of water vapour and the flame decomposition of the small amount of volatile matter produced at 120 C. is also resisied. Such decomposition may be described as abnormal decomposition.

When a cellulose acetate material is to be treated with a finishing composition the nature of such a finishing composition may vary widely according to the particular handle or drape required. Such finishing compositions include starch derivatives, gelatine, ureaformaldehyde resins, melamine-formaldehyde resins, acrylic polymers and in fact almost any synthetic polymeric material. A common finishing material used on cellulose acetate fabrics is based on gelatine.

When a gelatine based finish was applied to a flameresistant cellulose acetate fabric at an added weight of about 2 percent, the dressed fabric was no longer flameresistant. It was also found that a finish made from chlorinated rubber, applied to flame-resistant cellulose acetate fabric, caused the finished fabric to lose its flameresistance, although both the fabric and the finish by themselves were flame-resistant. Silicone rubber finishes REFERENCE SEARCl-l 'i'lllQ 'M which are heat-resistant also caused the otherwise flameresistant fabric to burn freely. This phenomenon indicated that it was possible to destroy all the advantages of a flame-resistant fabric by incorporatiing a dressing or finishing composition which was unsuitable, and it is an object of this invention to provide a process for the production of a finished textile material. based upon flame-resistant cellulose acetate whose flame-resistant properties are preserved after finishing.

According to the invention the process for finishing filaments, fibres, yarns, threads and fabrics of flame resistant cellulose acetate, which flame-resistant cellulose acetate has been produced by spinning from a solution containing cellulose acetate and a flame-proofing agent dispersed therein, comprises applying to the filaments, fibres, yarns, threads and fabrics a coating of an organic polymer composition which composition has a temperature of thermal decomposition not substantially greater than that of the flame-resistant cellulose acetate and which decomposes at its decomposition temperature to form soft and fusible products.

It is not generally necessary to apply very large amounts of finishing composition and a suitable amount is from about 0.1 percent to about 5.0 percent by weight of the weight of the filaments, fibres, yarns or fabrics. A preferred amount is from about 0.5 to about 3.0 percent. In view of the small amount of finishing composition used it is not essential that the finishing composition should itself be flame-resistant, since the flame-resistant properties of the cellulose acetate are quite sufficient to inhibit flaming of the finishing composition. However, it is preferred that the finish should itself be flame-resistant.

The criteria for the selection of the finishing composition are such as to ensure that the composition does not prevent the heat from the applied flame from reaching the flame-resistant cellulose acetate material freely. In this way the abnormal decomposition may take place at the lower temperature as described above. For this purpose, it is essential that the finish should decompose at a temperature not substantially greater than that at which the flame-resistant cellulose acetate decomposes, and that the decomposition product shall be soft and fusible so that the coating may melt away from the surface of the material and allow the heat and air to reach that surface so that the above described abnormal decomposition can take place. It will be apparent that a finish which decomposes at a sutficiently low temperature to give hard or horny decomposition products will protect the fibre from heat and air so that its temperature may run up rapidly to a high level and normal flame decomposition will take place.

The synthetic organic polymers which are used in the finishing of cellulose acetate in accordance with the invention include synthetic materials from at least four different groups.

The first group includes organic derivatives of cellulose which are film-forming but non-tacky at room tempera tures, eg. the non-tacky film-forming cellulose ethers such as ethyl cellulose.

The second group includes those polymers of vinyl and vinylidene monomers which form long carbon chains, at least a proportion of which carbon atoms are linked to acyloxy, carboxylic acid, carboxylic acid anhydride, carboxamide, N-substituted carboxamide, carbalkoxy and carbalkoxyalkyl groups. In the case of such copolymers other groups of different character which do not interfere with the aforesaid groups may also be present such as aromatic. and halo-aromatic groups. Examples of compounds are the non-tacky film-forming homopolymers and copolymers of vinyl acetate and methyl methacrylate,

the copolymers of partial alkyl esters of maleic acid with vinylidene monocyclic aromatic hydrocarbons such as styrene, copolymers of acrylic acid and methacrylie acid, polymers of alkyloxyalkyl methacrylates and co polymers of alkylated N-methylolacrylamide with vinyl-- .idene monocycli aromatic hydrocarbons.

The third group includes the alkylated aminoplastforming condensation products such as the alkylated dimethylolureas and the alkylated methylol urea-melamine co-condensation products.

The fourth. group includes halogenated polymeric hydrocarbons such as chlorinated synthetic rubber.

The temperature of decomposition of the flame-resistant cellulose acetate and of the dressing composition can be determined by heating 0.05 to 0.1 g. of the fabric or the solids of the dressing composition in an open test-tube, 3 inches long and 0.375 inch wide, at a rate of temperature rise of 5 C. per minute and noting the temperature at which a substantial carbonisation of the sample takes place, which temperature is referred to as the temperature of decomposition.

The nature of the decomposition products of the dress ing composition can be determined by heating a sample of the film-forming solids obtained from the dressing composition in an open test-tube 3 inches long and 0.375 inch wide by immersing the test-tube for 5 minutes in an oil bath maintained at the temperature of decomposition. The tube is then removed from the oil bath and the decomposed residue therein is probed with a wire. If the decomposition products are soft and fusible when hot, when so tested, it will be found that the dressing com-- position will have a satisfactory performance for use as a non-flammable finish for the flame-resistant cellulose acetate fabric. As a precaution, to guard against the possibility that there may be some unsuspected chemical interaction between the flame-resistant cellulose acetate and the finishing coating, a mixture of equal parts by weight of the flame-resistant cellulose acetate and the solids of the dressing composition may be subjected to the above-mentioned test at the temperature of decomposition to ascertain that the decomposition products of the mixure are soft and fusible.

The tests to determine the temperature of decomposition and the nature of this decomposition are carried out without exclusion of air from the samples of materials undergoing test.

If the decomposition products are otherwise than soft and fusible, i.e. if they form a hard black film on the test-tube or a hard sintered mass, then the dressing composition when applied to a flame-resistant cellulose acetate fabric will seriously impair its flame-resistant properties.

The flammability of the above-mentioned synthetic polymers is in no case substantially greater than that of the ordinary cellulose acetates and in those instances in. which the decomposition temperature of the polymer and/or the nature of the decomposition products produced therefrom is such that it does not accord with the requirements set forth above, the decomposition temperature may be lowered and the nature of the decomposition products produced rendered soft, generally soft and sticky, by the incorporation in the dressing composition of a tris(polybromoaliphatic)phosphate as referred to above in connection with the cellulose acetate spinning dope. It is believed that the soft products produced on decomposition of the cellulose acetate and those produced on decomposition of the dressing become fused together. Since the proportion of flame-proofing agent exceeds the minimum required to secure the desired flame-resistant properties in the cellulose acetate, it suflfices to impart flame-resistance to the small per" centage of additional material becoming fused therewith.

Ethyl cellulose is an example of a dressing material which is not readily fusible on heating but, when admixed with increasing quantities of tris(dibromopropyl) phosphate or with tricresyl phosphate, it becomes more and more fusible and, when the former is admixed therewith, less and less flammable. Thus, ethyl cellulose may form the basis of a satisfactory dressing composition from which will be deposited a coating layer which will fulfill the requirements of the invention. A satisfactory dressing composition may similarly be obtained from a butyl ether of a methylolurea by admixture with the tris(dibromopropyl)phosphate. In all cases it is preferable that the compound which is added to the essential coating component of the dressing composition should be compatible therewith.

A preferred cellulose acetate fabric is formed from yarns, threads, filaments or fibres produced from a cellulose acetate spinning dope containing a tris(polybromoaliphatic)phosphate having a bromine content a bromine content of at least 50 percent by weight in an amount of 2.5 to percent by weight of the cellulose acetate, preferably in an amount of from 5 to 7 percent; the organic polymer or polymer composition is preferably applied in the form of a solution of emulsion, or dispersions thereof may be employed in each case dis solved or suspended in a volatile liquid carrier.

Thus, for example, the dressing compositions may be applied to the cellulose acetates in solution in water, as an aqueous solution of an ammonia or volatile amine salt thereof when a polymer containing free carboxyl groups or carboxylic acid anhydride groups is used, in solution in an organic solvent in which the cellulose acetate employed is substantially insoluble or in the form of an aqueous emulsion or suspension. The tris(polybromoaliphatic)phosphates are readily soluble in certain organic solvents such as toluene and xylene in which the cellulose acetates are substantially insoluble, and such solvents may remove some of these compounds from the fabric it they are used.

The dressing compositions may be applied to the filaments, fibres, yarns, threads or fabrics of cellulose acetate by passing through a bath containing a solution, suspension or emulsion containing the dressing composition in the form in which it is to be applied to the material to be treated. On emerging from the bath, which may conveniently be maintained at substantially room temperature, the impregnated material is passed between rollers to remove excess of the composition and ensure uniform impregnation. The concentration of the bath employed should be correlated with the pressure applied on passage between the rollers to secure the desired take-up of the film-forming ingredients. The material is then dried.

The invention also includes within its scope flame-resistant, filaments, fibres, yarns, threads and fabrics of a cellulose acetate having uniformly distributed therethrough a flame-proofing agent formed by spinning from a cellulose acetate, for example up to 10 percent, preferably 5 to 7 percent, by weight of the cellulose acetate of a flame-proofing agent which is preferably tris(polybromoaliphatic)phosphate, the said filaments, fibres, yarns, threads and fabrics having a coating of a synthetic organic polymer or polymer-containing composition, the flammability of which polymer is not substantially greater than the flammability of the cellulose acetate Whilst the temperature of thermal decompositon of said polymer or polymer-containing composition does not substantially exceed that of the flam-proof cellulose acetate and th decomposition products of the polymer or polymer-containing composition, at the temperature of decomposition, are soft and may be sticky. Other flame-proofing agents which may be used are tris(chloroethyl)phosphate, aluminium pyrophosphate and the materials sold under the tradename Phosgard which are complex organic halogencontaining polyphosphonate esters (those containing at least some bromine and having a total halogen content of at least 50 percent by weight are preferred).

Whilst it is often convenient to apply the finishing treatment to a fabric woven from one or more fiame-proofed cellulose acetates, it should be appreciated that the com positions comprising a film-forming synthetic organic polymer may readily be applied to fiame-proofed yarns as a size prior to weaving; such yarns may have been dyed. The woven cloth is not then desized after weaving. Examples of such materials are a bridal satin and a poult taffeta which, when Woven, do not require the application of a further finish, are not spotted by water and do not become raggy after dry cleaning.

Such sizes may be applied on a conventional sizing or slashing machine. The amount of solids taken up by the yarns is normally higher than that applied as a finishing composition and may be from 2.5 to 6 percent, preferably 3 to 4 percent, of the weight of the yarns. The sizing composition may be more con centrated than the finishing composition, e.g. from 5 to 7 percent, in order to permit the larger tape-up envisaged from the sizing bath, and the bath itself may be held at a temperature above room temperature, e.g. from 40 to 50 C. Additional ingfedients may be present in such a sizing bath in order to modify the hand of the woven fabric. Thus, the addition of up to 25 percent of urea based upon the weight of an ester polymer, such as a vinyl acetate-carboxylic acid copolymer, to the sizing bath has been found to soften the hand of a woven flame-resistant cellulose acetate fabric.

With respect to the amount of synthetic polymeric material or composition containing such material which is present on the surface of the filaments, fibres, yarns, threads or woven material, it will be appreciated that this will depend upon the stage at which it is applied and the purpose or purposes which it is intended to serve. From 0.1 to 10 percent of the weight of the material being treated may be used. In those cases in which the higher proportions of finish are used it is desirable that the dressing or sizing used should include a flameproofing agent.

When the treatment intended is the application of a final dressing it will be appreciated that all the pretreatments customarily employed, such as desizing and scouring, will first be carried out in the usual manner.

The following examples are given to illustrate the nature of the invention.

EXAMPLE 1 For application to a secondary cellulose acetate yarn or fabric, which cellulose acetate had substantially uniformly dispersed therethrough 7 percent of tris(dibromopropyl)phosphate and had a decomposition temperature in the range of 220 C., a finishing composition containing polyvinyl acetate is used. This composition contains 2 parts by weight of polyvinyl acetate, 1 part of tris(dibromopropyl)phosphate and 1 part of zinc resinate. A 3 percent solution of this finishing composition in toluene is made. The cellulose acetate material is passed therethrough and then between rollers by means of which the take-up is adjusted to 60 percent of the weight of the cellulose acetate. The treated material is then dried.

EXAMPLE 2 A fiame-proofed primary cellulose acetate fabric was used, the yarns of which had uniformly dispersed there-- EXAMPLE 3 The procedures of Examples 1 and 2 are repeated using a finishing composition containing 3 parts of ethyl cellulose and 1 part of the tris(dibromopropyl)phosphate.

EXAMPLE 4 A coating composition is prepared from 10 parts by Weight of a butylated urea-formaldehyde condensation product (supplied as a viscous solution of 66 percent total solids content), 10 parts of Zinc resinate and 1.75 parts of tris(dibromopropyl)phosphate. A 3 percent solution in toluene was prepared and applied to the same kind of flame-resistance cellulose acetate as that used in Example 1: the subsequent procedure was the same as that described in that example.

EXAMPLE 5 The procedure of Example 4 is repeated using a coating composition prepared from 1 part by weight of chlo rinated rubber and 3 parts of tris(dibromopropyl)phosphate. A 2 percent solution of this composition was similarly prepared and used.

EXAMPLE 6 Nine parts by weight of a textile finishing emulsion which is reputed to contain a copolymer of a butylated methacrylamide of the kind described in French Patent No. 1,162,967, Example 15, and which contains 33 percent by weight of solids is admixed with 1 part of tris- (dibromopropyl)phosphate dispersed in water. Additional water is added until the solids content is reduced to 3 percent and a flame-proofed cellulose acetate of the kind used in Example 1 is then passed through the resulting bath. The further treatment is as described in Example 1.

EXAMPLE 7 The procedure of Example 6 is repeated using four parts by weight of a vinyl acetate-vinyl chloride copolymer emulsion of 55 percent solids content admixed with 1 part of tris(dibromopropyl)phosphate and dispersed in water to 3 percent total solids content.

EXAMPLE 8 Each of the following emulsions was used in turn:

(a) An emulsion of a copolymer of vinyl acetate and 2-ethylhexyl acrylate (56 percent total solids) which is diluted with 18 parts by weight of water:

(b) An emulsion of a copolymer of vinyl acetate and vinyl caproate (56 percent total solids) which. is diluted with 18 parts by weight of water;

(c) An emulsion of a copolymer of vinyl acetate with an unsaturated acid sold under the registered trademark Vinamul 6000 (56 percent total solids) which is diluted with 27 parts by weight of water;

(d) An emulsion of poly-2-ethoxyethyl methacrylate (33 percent total solids) which is diluted with 16 parts by weight of water;

(e) An emulsion of polymethyl methacrylate (33 percent total solids) which is diluted with parts by weight of water, and. was diluted with sufiicient water to produce dressing composition having a. solids content of 3 percent by weight. Primary and secondary fiame-proofed cellulose acetate yarns and fabrics were passed through the resulting baths and then between rollers by means of which the take-up was limited to 60 percent of the dry weight of the fabric. The treated yarns and fabrics were then dried.

As applied, emulsion (a), (b) and (e) have a substantially 3 percent total solids content whilst emulsions (c) and (d) have a substantially 2 percent total solids content.

EXAMPLE 9 Two parts of a. solid polymer of styrene and maleic anhydride and/or a partial allcyl ester of maleic acid sold under the registered trademark Stymer LP is dissolved, with heating, in water containing 0.24 part of aqueous ammonia. sp. gr. 0.880. Sufficient water to make a total of 100 parts is then added.

This solution is applied to a primary cellulose acetate fabric by passage through a bath thereof and then between a. pair of rollers adjusted to limit the take-up to 60 percent of the dry weight of the fabric. The treated material is then dried. On heating and drying ammonia. is evolved and the polymer becomes insoluble in water.

EXAMPLE 10 Three parts of an alkali soluble copolymer of vinyl acetate sold under the trade name Bevaloid is dissolved, with heating, in water containing 0.12 part of aqueous ammonia sp. gr. 0.880. Sufficient water to make a total of 100 parts is then added. The subsequent procedure is the same as in Example 9. On heating and drying ammonia is evolved and the polymer becomes insoluble in water.

The decomposition temperatures of the polymers or of the polymer-containing compositions remaining upon the cellulose acetate after drying in all the above examples are within the range to 220 C, and all yield decomposition products which. are soft and, in most cases, sticky at their decomposition temperatures. Films cast therefrom are either non-flammable or they have a low degree of flammability not substantially exceeding that of the cellulose acetates employed.

Yarns and fabrics when subjected to the several treat ments described in the examples were found to have a satisfactory degree of non-flammability. They do not propagate a flame when out of contact with an externally applied flame and do not exhibit afterglow when tested in accordance with the method described in British stand ard specification No. 2,963/58.

What is claimed is:

1. In a process for finishing filaments, fibres, yarns, threads and fabrics of flame-resistant cellulose acetate which has been produced by spinning from a solution con-- taining cellulose acetate and a flame-proofing agent dis-' persed therein, the improvement which comprises applying to the filaments, fibres, yarns, threads and fabrics a coating of an. organic polymer composition which com position has a temperature of thermal decomposition within the range of 180 to 220 C. and not substantially greater than that of the flame-resistant cellulose acetate and which decomposes at its decomposition temperature to form soft and fusible products.

2. The improvement as claimed in claim 1 in which the amount of organic polymer composition applied is from 0.1 percent to 5.0 percent by weight of the weight of the fiame-proof cellulose acetate material.

3. The improvement as claimed in claim 1 in which the organic polymer composition used for coating is itself flame-resistant.

The improvement as claimed in claim 1 in which the organic polymer composition used for coating is selectcd from the group consisting of film-forming cellu lose ethers, homopolymers and copolymers of vinyl and vinylidene monomers, amino-aldehyde condensation prod ucts and halogenated polymeric hydrocarbons.

5. The improvement as claimed in claim 4 in which. the coating composition also contains a modifier of tris- (polybromoaliphatic)phosphates.

6. The improvement as claimed in claim 4 in which the coating composition also contains tris(dibromopropyl)phosphate.

7. The improvement as claimed in claim 1 in which the flame-resistant cellulose acetate has been produced. by spinning from a solution containing cellulose acetate and a flame-proofing agent of. tris(polybromoaliphatic) phosphates.

8. The improvement as claimed in claim I in which the flame-resistant cellulose acetate has been produced by s inning from a solution containing cellulose acetate and tris(dibromopropyl)phosphate.

9. Flame-resistant cellulose acetate coated with an organic polymer composition, the flame-resistant cellulose acetate being the product of spinning a solution containing cellulose acetate and a flame-proofing agent and the organic polymer coating having a temperature of thermal decomposition within the range of 180 to 220 C. and not, substantially greater than that of. the flame-resistant cellulose acetate, and decomposing at its decomposition temperature to form soft and fusible products,

10. Flame-resistant cellulose acetate coated with an or-= ganic polymer composition, as claimed in claim 9, in which the organic polymer coating is selected from the group co sisting of film-forming cellulose ethers, homopolymerlsjand copolymers of vinyl and vinyldene monj mers, a ino-aldehyde condensation products and hal genated polymeric hydrocarbons.

11., Flame-resistant cellulose acetate coated with an organic polymer composition, as claimed in claim 10, in which the organic polymer coating also contains a 'modi fier of tris(polyhromoaliphatic)phosphates.

12. Flame-resistant cellulose acetate coated with an or=- ganic polymer composition, as claimed in claim 10, in which the organic polymer coating also contains tris(dibromopropy1)pho'sphate.

13. Flame-resistant cellulose acetate coated with an organic polymer composition, as claimed in claim; 9 in which the flame-resistant cellulose acetate is the product of spinning a solution containing cellulose acetate and a flame-proofing agent of tris(polybromoaliphatic)phos=- phatesa 14. Flame-resistant cellulose acetate coated with an or= ganic polymer composition, as claimed in claim 9 in which the flame-resistant cellulose acetate is the product of spinning a solution containing cellulose acetate and tris(dibromopropyl)phosphate,

References Cited UNITED STATES PATENTS 1,936,985 11/1933 Lommel et a1,

2,574,515 11/1951 Walter et a1. 117136 X 2,660,543 11/1953 Walter et a1 117-136 X 2,779,691 1/1957 Loukomsky 117-136 X 2,876,117 3/1959 Jackson et a1 117-137 X 2,876,118 3/1959 Jackson 117-137 X 2,953,480 9/ 1960 Burnell,

3,266,918 8/1966 S chappel et al. l06-177 X 3,321,330 5/1967 Mohney 117145 X WILLIAM D. MARTIN, Primary Examiner 20 H L GWINNELL, Assistant Examiner Us c1. X.R. 117- 145; 106-15, 177 

